This invention relates to the field of G force acceleration effect sensing accomplished by way of visual field and psychomotor tracking performance evaluation in a test subject.
When a human subject is exposed to increasing G force acceleration, a well-established sequence of degradation changes in the subject's blood circulation occur. In modern high-performance aircraft and spacecraft, these hemodynamic changes require consideration in order that a human operator remain physically able to function as an aircraft pilot or as a performer of technical functions. The change in human blood circulation is particularly severe in the case of +GZ axis G forces, forces directed downward from the head and tending to collect blood in the lower extremities of a subject's torso so that the blood supply to the brain and eye retina are diminished. Another severe condition results from -GZ axis acceleration forces which tend to collect excessive blood quantity and pressure in the brain and produce a red-out response. Supplemental body pressure apparatus and test subject physical "exercises" which tend to increase the tolerance of acceleration forces have been used in military equipment for some time; the G-suit is a well-known example of such apparatus and is particularly effective for increasing the tolerance of +GZ axis forces. G force acceleration in the other coordinate directions, that is, along the X axis, tending to press a test subject more firmly against a seat back or along the +Y axis, tending to move the subject to his left, are also detrimental to blood circulation to lesser degrees.
The progressive reduction of blood circulation particularly in response to increasing GZ forces results in several correspondingly progressive physiological effects, including a dimming of the subject's vision or "gray-out", a narrowing of the subject's visual field or vision tunneling, a total loss of vision or "blackout" and ultimately a loss of consciousness.
As a result of differences between the intra-ocular pressure and intracranial pressure in a human body, blood circulation to the eye is diminished prior to circulation to the brain, and a loss of vision, particularly far peripheral vision, generally precedes loss of consciousness in a G force test subject. This established order of circulatory disruption therefore provides a convenient and repeatable means by which a test subject's response to G forces can be objectively evaluated and by which the onset of undesirable effects in a test subject can be detected.
Exposure to G force acceleration is also known to degrade a test subject's psychomotor tracking performance in addition to the above-described circulatory or hemodynamic effects. The ability of a test subject to perform a task requiring both visual and psychomotor capabilities is therefore a doubly useful tool in assessing the degree of tolerance the subject exhibits to acceleration G forces. The combination of visual and psychomotor capability can therefore be desirably evaluated in a G force test environment by assigning a test subject to perform tasks which involve visual input and motion output; preferably the expected performance should allow measuring both the extent and the rate of degradation in the subject's visual field and psychomotor tracking ability.
Arrangements for combining a measurement of a test subject's visual field and psychomotor tracking ability under the influence of acceleration G forces are known in the art as is evidenced, for example, by the patent of Malcolm Cohen, U.S. Pat. No. 4,421,393 and the several G force effect measuring systems therein described.
The Cohen invention concerns a visual field perimeter and psychomotor tracking performance measuring apparatus for use with a human test subject centrifuge operated by the U.S. Navy. In the Cohen invention a semicircular array of light emitting diodes (LEDs) is arranged to subtend the lateral field of view of the test subject and is excited such that pairs of opposed diodes symmetrically located about a central viewing axis are sequentially illuminated at a programmed rate and in an inward or outward progressing sequence. The test subject in the Cohen apparatus employs a control stick to generate a nulling signal that maintains a desired peripheral field pair of light emitting diodes illuminated. The Cohen apparatus relies upon the test subject performing a manipulation of the control stick in response to peripheral vision diminishing with increased acceleration forces. The Cohen apparatus also contemplates the use of a pseudo-random pattern of LED excitation without, however, specifying the precise nature of the random signal or indicating how it is generated.
A conceptual advantage of the present invention over the Cohen apparatus concerns the achieved reduction in the ability of a test subject to bravado, enhance or cheat the measurement system by artificially indicating a better response to the G force effects than he actually experiences. In the present invention, the test subject is required to see the position of the driving visual stimulus in order to position a responding visual stimulus properly. In the absence of seeing the driving visual stimulus, the test subject is precluded from making any response and thus from enhancing his measured tolerance of the G force.
The Cohen patent also describes several prior art visual testing arrangements including one in which a lamp located in the test subject's visual periphery is randomly illuminated and the test subject is required to immediately press a button to extinguish the lamp. As indicated in the Cohen patent, this arrangement does not test the subject's visual field and the rate at which it collapses, nor does it measure the psychomotor tracking ability of the subject.
Additional distinctions of the present invention over the Cohen apparatus concern arrangement of the display in the present invention, including the two arrays of visual stimulus elements and the circuitry used for driving display LED elements.
Another example of prior patent art relating somewhat to the present invention is found in the patent of C.L. Kuether et al, U.S. Pat. No. 4,255,022, concerning an improved "perimeter" apparatus of the type used for vision testing in a medical examination environment. In the Kuether invention microprocessor techniques are employed to improve an existing perimeter device through incorporation of an electronically-controlled silent shutter and an electronically controlled operator lead-through system. The Kuether apparatus is of course unconcerned with testing for the effects of G force acceleration.
An example of prior art apparatus requiring the cooperation of a subject with a visual stimulus-generating machine is found in the patent of David J. Hall, U.S. Pat. No. 4,169,592 wherein there is described an electronic reflex challenging game requiring a player to respond to a randomly actuated one of three possible light bulbs within an increasingly shortened response time. The Hall apparatus is unconcerned with the player's physical environment and additionally involves only a race against time as the physical trait to be measured in the test subject.
Another example of prior patents concerning visual testing is found in the patent of J. R. Lynn et al, U.S. Pat. No. 3,705,003 n which a test subject operates a joystick control in response to an unpredictable or random sequence visual stimulus display in order to achieve mapping of his vision capability. The Lynn apparatus teaches the use of a cathode ray tube display which is arranged in a 64.times.64 or higher resolution grid and employs a four-bit intensity determining word at each grid location. As indicated at column 10, line 34 in the Lynn patent, the test subject is expected to move the joystick control in the general direction of the bright spot he has observed on the cathode ray tube screen. The Lynn apparatus defines a measurement tool called an error sector and determines if the test subject's response comes within an allowable number of error sectors of the cathode ray tube displayed spot.
The Lynn apparatus is of course intended for use in a medical testing environment in contrast with applicant's environment of acceleration G force effect testing; the Lynn apparatus moreover is silent with respect to providing feedback to the test subject as to the results of his joystick control manipulation. The Lynn apparatus also appears to depend on human operator generation of the random data used for test spot location.
Another example of prior art peripheral vision testing apparatus is found in the patent of R. J. Beitel, Jr. U.S. Pat. No. 2,316,042 which discloses an adjustable perimeter testing device used for medical vision testing and employing manually movable mechanical target or visual stimulus member. The Beitel apparatus includes the familiar perimeter screen and moving target concept, and further contemplates the use of multicolored targets. The Beitel apparatus is also intended for use outside the G force acceleration testing environment and employs manual positioning of the visual stimuli.